I agree with the answer from rlb.usa that she might be in pain. Additionally, she might be unsettled by the change in her relationship with her owner caused by your relationship with her owner.
You are basically a new member of the pack, so the hierarchy was disturbed. You boyfriend might interact with her differently or maybe less than usual, which unsettles her more. Then add the move into a new house. That's all very stressful for a dog.
For a dog, our human world is very complex and chaotic. If she has the feeling that her owner is no longer asserting his dominance, she might feel obliged to become the pack leader herself. Have a look at this answer to get an idea why this might cause aggressive behavior and what to do against it.
Then I advice you to buy a crate for the dog, if you don't have one yet. The crate must be big enough for her to stand up and lay down comfortably in and it must have a pillow or blanket to be a comfortable place for her.
This will become her safe haven. Her crate is her place alone, you don't go in there. The crate should always be associated with positive feelings, so you may sit down and pet her in the crate and give her treats. She must never be scolded or reprimanded while being in her crate.
Then start training with her:
- Get her used to being locked into the crate.
- She should sleep in the crate every day.
- Train with her to send her into the crate by command.
- Whenever she growls at someone or shows bad behavior, send her into the crate and lock her in.
- Invite your neighbors onto your property but explain that your dog might growl. If she does growl, lock her into the crate.
- Depending on her behavior, you can let her out of the crate after 10-20 minutes (give her time to calm down) or after your visitors left.
This approach was recommended to us by a professional dog psychologist / dog whisperer. Our dog was mistreated as a puppy and badly socialized. He is extremely insecure when interacting with humans, which often turns into aggression. It's a great way to give him time to process what's going on around him and see that the visitors are no danger to the pack.